The present invention relates to fluid delivery systems, and more particularly relates to injectors and nozzles therefore, useful for dispensing liquid fuel in gas turbine engine applications.
The nozzle in a fluid delivery system is an important component of the system. In aircraft applications, for example, where fuel is delivered through the nozzle for combustion in a combustor, it is desirable to reduce emissions, provide better spray patternization and provide more uniform combustion of fuel.
One such nozzle is illustrated and described in U.S. Pat. No. 5,740,967, which is owned by the assignee of the present invention. In this nozzle, liquid fuel enters a swirl chamber, where it is caused to move in a vortex toward the center of the chamber, and then exit the chamber and be delivered through a spray orifice, forming a hollow cone spray. The swirl chamber and orifice are formed by chemical etching one or more plates. The etching produces a nozzle with very streamlined geometries resulting in reductions in pressure losses and enhanced spray performance. The chemical etching process is easily repeatable and highly accurate, and can produce multiple nozzles on a single plate for individual or simultaneous use.
One embodiment of this type of nozzle is shown in U.S. patent application Ser. No. 09/794,490, for xe2x80x9cIntegrated Fluid Injection and Mixing Systemxe2x80x9d, filed Feb. 27, 2001, which is also owned by the assignee of the present invention. In this embodiment, the nozzles are located in an injector, and air passages are provided through the plates in surrounding relation to the nozzles. The air passages direct air radially inward in a swirling manner around the fuel sprays to provide a homogeneous fuel-air mixture. It has been found that this injector is particularly useful in reducing Nitrogen Oxide (Nox) and Carbon Monoxide (CO) emissions, and the spray is well dispersed for efficient combustion.
The power generation industry is faced with increasingly stringent emissions requirements for ozone precursors, such as nitrogen oxides and carbon monoxide. To achieve lower pollutant emissions, gas turbine manufacturers have adopted lean premixed (LP) and lean direct injection (LDI) combustion as a standard. LP combustion achieves low levels of pollutant emissions without additional hardware for steam injection or selective catalytic reduction (SCR). By premixing the fuel and air, localized regions of near stoichiometric fuel-air mixtures are avoided, and a subsequent reduction in thermal NOx can be realized. To achieve lower levels of NOx emissions, homogeneous fuel-air mixture distributions are necessary. To achieve mixture homogeneity, a spatially resolved, multipoint fuel injection strategy is often required. Relative to single-point fuel injection, multi-point fuel injection offers numerous advantages, such as significantly shorter mixing length and time scales. These shorter mixing scales can result in shorter premixer lengths and a significantly lower propensity for flashback and autoignition.
Another factor is cooling. When the fuel is ignited, the engine temperature increases, which can lead to coking of surfaces and the interruption of fuel flow. Cooling passages and heat shields can be provided, however this can add to the size and weight of an engine, and generally make it more difficult to manufacture (and repair) the engine.
As such, it is believed that there is a further demand for an improved injector with a multiple spray nozzle arrangement which combines many of the advantages of the above nozzles, but which has a more compact form and good thermal management. While these issues are primarily important in fuel injectors for gas turbine engines, it is believed that the same issues arise in other liquid fuel applications as well, such as in industrial power applications, as well as generally in other fluid applications.
The present invention provides a novel and unique injector for dispensing fluid, and in particular, an injector for dispensing liquid fuel in gas turbine applications. The injector has multiple nozzles for improved fuel delivery, but has a compact form, which reduces the weight and size of the engine, and good thermal management. The injector preferably has passages which are formed by chemical etching, for efficient fuel flow. The present invention is directed towards achieving fuel-air mixture homogeneity by using an easy and affordable multipoint injection strategy. The nozzle is actively cooled, which provides good atomization performance, fast droplet dispersion, and a mixture homogeneity that it is believed is not readily attainable with conventional nozzle technology.
According to a preferred embodiment of the present invention, the injector includes a plurality of flat, circular plates which are stacked and bonded together in surface-to-surface adjacent relation. The plates have multiple internal passages to provide fuel delivery and cooling of the injector, and cooling of the nozzles. The fuel delivery passages are preferably formed by chemical etching for efficient fuel flow through the injector. At least some of the cooling passages are also formed by etching.
A pair of fuel delivery plates are arranged in adjacent, surface-to-surface relation with each other, and define a fuel cavity therebetween. The upstream fuel plate includes an opening along the central axis to receive an elongated fuel tube. Both plates also include a plurality of spokes, which extend radially outward from the central axis, in evenly, spaced-apart relation to one another, with the spokes from one plate in adjacent, surface-to-surface relation with the opposing spokes from the adjacent plate. A fuel passage is provided between each of the opposing spokes, leading radially from the fuel cavity to a fuel delivery opening at the distal end of each spoke. The fuel delivery openings are oriented to deliver the fuel axially from the spokes. The fuel tube delivers fuel to the fuel cavity between the plates, where the fuel is directed outwardly along the individual passages to the delivery openings. Downstream plates are provided to shape the fuel into appropriate sprays for ignition. Preferably, the downstream plates also have passages formed by chemical etching, which define multiple simplex nozzles around the injector and shape the fuel streams into hollow conical sprays. The sprays combine in a homogeneous mixture for reduced emissions, good patternization, and improved combustion.
To cool the fuel delivery passages during engine operation, an upstream cooling plate assembly is provided. The cooling plate assembly includes a stack of plates that direct air against the upstream surface of the upstream fuel delivery plate, and radially outwardly along the spokes of the upstream plate. The cooling air then passes downstream around each of the hollow core sprays. The air preferably is delivered through an air tube, which runs concentric with and outwardly surrounds the fuel delivery tube. The air tube also cools and thermally protects the fuel passing through the fuel tube.
Thus, as described above, the present invention provides an injector, particularly useful for dispensing liquid fuel in gas turbine applications, which is an improvement on the previous designs. The injector has multiple nozzles for improved fuel delivery, and has a compact form, which reduces the size and weight of the engine, and good thermal management. The injector preferably has passages which are formed by chemical etching, for efficient fluid flow through the injector. The actively cooling nozzle provides good atomization performance, fast droplet dispersion and good fuel-air mixture homogeneity.
Further features of the present invention will become apparent to those skilled in the art upon reviewing the following specification and attached drawings.